Regarding conventional LED (light emitting diode) chips, normally, silicon dioxide (SiO2) is used to form a surface insulating layer, and a chromium/platinum/gold (Cr/Pt/Au) multilayer serves as an electrode structure (as shown in FIG. 1). Alternatively, an aluminum (Al) reflective layer is further inserted to form a Cr/Al/Pt/Au multilayer which serves as a reflection electrode structure. In the aforesaid electrode structures, Au is used as a metal material for wire bonding during packaging, but the adhesion between Au and the semiconductor protection material (e.g. SiO2) is poor. Namely, during the production of a LED chip, the parts of the SiO2 insulating layer in contact with the Au layer of the electrode structure might easily separate from the electrode structure, or might be detached from the electrode structure by a pulling or pushing force applied. Accordingly, the SiO2 insulating layer cannot provide sufficient protection for the electrode structure, such that the LED chip might undergo abnormality arising from aging of packaging, e.g. migration of the Cr layer, oxidation of the Al layer, lumen depreciation, etc. Particularly, in the absence of a satisfactory protection layer, a display chip might easily undergo aerosol contamination that induces undesired permeation of organic substances and water vapor into the electrode structure, which in turn leads to electromigration of metal ions and even serious aging and other abnormality.
In order to enhance the structural tightness, an electrode structure disclosed in CN 103238223 A is produced by depositing a metal material having stronger adhesion to SiO2, such as nickel (Ni), Ti (titanium), or titanium-tungsten (TiW), on a surface layer of an electrode. It is disclosed in CN 103238223 A that the Ni layer is subjected to etching to expose the Au layer for the same to serve as a surface electrode. For example, a dry etching process, such as inductively coupled plasma (ICP) etching, may be used. However, the aforesaid process might easily damage the Au layer and result in dark spots, such that a gold wire for wire bonding might not be securely bonded. Furthermore, as shown in FIG. 2, the SiO2 protective layer disposed over the Ni layer (i.e. the uppermost layer) of the five-layered electrode structure might be easily detached from the electrode structure by a pulling or pushing force applied during wire bonding for packaging (please note that the cloud-shaped substance in FIG. 2 represents a detached part of the SiO2 protective layer), thereby inducing malfunction of the chip during use or aging.